Flooded lead-acid battery and method of making the same

ABSTRACT

Positive active material pastes for flooded deep discharge lead-acid batteries, methods of making the same and lead-acid batteries including the same are provided. The positive active material paste includes lead oxide, a sulfate additive, and an aqueous acid. The positive active material paste contains from about 0.1 to about 1.0 wt % of the sulfate additive. Batteries using such positive active material pastes exhibit greatly improved performance over batteries with conventional positive active material pastes.

CROSS REFERENCE TO RELATED APPLICATION(S)

This application is a continuation of U.S. patent application Ser. No.13/760,673 filed on Feb. 6, 2013, which is a continuation of U.S. patentapplication Ser. No. 12/275,158, filed on Nov. 20, 2008, now issued asU.S. Pat. No. 8,404,382, which claims the benefit of U.S. ProvisionalApplication No. 61/043,377, filed on Apr. 8, 2008, the entire contentsof which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to flooded or wet cell lead-acidelectrochemical batteries, and more particularly to positive activematerial pastes for use in such batteries and to methods of making andusing the same.

BACKGROUND OF THE INVENTION

A typical flooded lead-acid battery includes positive and negativeelectrode grids and an electrolyte. The electrode grids, while primarilyconstructed of lead, are often alloyed with antimony, calcium, or tin toimprove their mechanical characteristics. Antimony is generally apreferred alloying material for deep discharge batteries.

In a flooded lead-acid battery, positive and negative active materialpastes are coated on the positive and negative electrode grids,respectively, forming positive and negative plates. The positive andnegative active material pastes generally comprise lead oxide (PbO orlead (II) oxide.) The electrolyte typically includes an aqueous acidsolution, most commonly sulfuric acid. Once the battery is assembled,the battery undergoes a formation step in which a charge is applied tothe battery in order to convert the lead oxide of the positive plates tolead dioxide (PbO₂ or lead (IV) oxide) and the lead oxide of thenegative plates to lead.

After the formation step, a battery may be repeatedly discharged andcharged in operation. During battery discharge, the positive andnegative active materials react with the sulfuric acid of theelectrolyte to form lead (II) sulfate (PbSO₄). By the reaction of thesulfuric acid with the positive and negative active materials, a portionof the sulfuric acid of the electrolyte is consumed. However, thesulfuric acid returns to the electrolyte upon battery charging. Thereaction of the positive and negative active materials with the sulfuricacid of the electrolyte during discharge may be represented by thefollowing formulae.

Reaction at the negative electrode:Pb (s)+SO₄ ²⁻ (aq)

PbSO₄ (s)+2e ⁻

Reaction at the positive electrode:PbO₂ (s)+SO₄ ²⁻ (aq)+4H⁺+2e ⁻

PbSO₄ (s)+2(H₂O) (l)As shown by these formulae, during discharge, electrical energy isgenerated, making the flooded lead-acid battery a suitable power sourcefor many applications. For example, flooded lead-acid batteries may beused as power sources for, electric vehicles such as forklifts, golfcars, electric cars, and hybrid cars. Flooded lead-acid batteries arealso used for emergency or standby power supplies, or to store powergenerated by photovoltaic systems.

To charge a flooded lead-acid battery, the discharge reaction isreversed by applying a voltage from a charging source. During charging,the lead sulfate reacts with oxygen molecules from ionized water toproduce lead and lead dioxide. The lead dioxide is deposited on thepositive electrode and the lead is deposited on the negative electrode.

The lead dioxide deposited on the positive electrode is known to existin two different crystalline structures, α-PbO₂ and β-PbO₂. Of these,α-PbO₂ tends to have a larger size crystal providing lower surface areaover β-PbO₂ which has a smaller size crystal with higher surface area.In batteries, the larger crystal size and lower surface area of α-PbO₂tends to lower initial battery capacity, but provides longer lifecompared to the smaller crystal size and larger surface area of β-PbO₂which tends to provide higher initial battery capacity, but shorterbattery life. Upon initial formation, the positive active material pasteof a typical deep discharge flooded lead-acid battery tends to exhibitan α-PbO₂ to β-PbO₂ ratio of about 1.2 or higher.

The addition of tin sulfate to positive electrode in flooded batteriesis known, but is generally limited to use in batteries that use positiveelectrodes made of lead-calcium alloys. Batteries using lead-calciumalloy positive electrode grids are known to suffer from the developmentof a poorly defined corrosion layer at the surface of the grid which canlimit battery life. It has been suggested that the addition of tin tothe alloy from which the grid is made, or the application of tin to thesurface of a grid will form a tin-enriched layer at the surface of thegrid, and in doing so, will improve the properties of the corrosionlayer at the interface surface of the grid. However, it is alsogenerally recognized that positive electrode grids of a lead-antimonyalloy have well defined corrosion layers, and therefore, would notbenefit from the formation of a tin-enriched layer. Moreover, it is alsogenerally recognized that any tin provided at the positive electrodegrid will tend to migrate to the negative electrode grid during batteryuse, and in doing so, will change the half potential of the negativeelectrode grid and adversely affect the recharge characteristics of thebattery.

SUMMARY OF THE INVENTION

An embodiment of the present invention is directed to an improvedpositive active material paste for a flooded deep discharge lead-acidbattery of the type that includes lead-antimony alloy positive electrodegrids. Such a positive active material paste includes lead oxide, ametal sulfate additive, and sulfuric acid. The positive active materialpaste may optionally include a binder such as polyester fiber. Accordingto one embodiment, the metal sulfate is tin sulfate. For such anembodiment, the metal sulfate additive may be present in the paste in anamount of about 0.2 wt % or less on a dry basis. In another embodiment,the tin sulfate additive is present in the paste in an amount of about0.18 wt % on a dry basis. Upon battery formation, the lead oxide of thepaste is converted to lead dioxide, and it is believed the metal sulfateis similarly converted to an oxide of the metal.

In an embodiment of the invention, the molar ratio of lead to metal (ormetal oxide) for the positive active material paste ranges from about200:1 to about 825:1. In one exemplary embodiment, the molar ratio oflead to the metal (or metal oxide) is greater than about 450:1(corresponding to an initial amount of tin sulfate (when tin sulfate isthe additive) of about 0.22 wt % on a dry basis). In another embodiment,the lead to metal additive molar ratio of the positive active materialpaste is between about 450:1 and about 650:1 (corresponding to aninitial amount of tin sulfate (when tin sulfate is the additive) rangingfrom about 0.15 to about 0.22 wt. % on a dry basis). In yet anotherembodiment, the lead to metal additive molar ratio of the positiveactive material paste is about 500:1 (corresponding to an initial amountof tin sulfate (when tin sulfate is the additive) of about 0.2 wt % on adry basis).

For embodiments where tin is used as the metal additive, the tin may beprovided to the paste as tin sulfate. For such embodiments, the lead totin weight ratio of the positive active material paste may be greaterthan about 800:1 (corresponding to an initial amount of tin sulfate ofabout 0.22 wt % on a dry basis). In another embodiment, the lead to tinweight ratio of the positive active material paste is between about800:1 and about 1100:1 (corresponding to an initial amount of tinsulfate ranging from about 0.15 to about 0.22 wt % on a dry basis). Inyet another embodiment, the lead to tin weight ratio of the positiveactive material paste is about 900:1 (corresponding to an initial amountof tin sulfate of about 0.19 wt % on a dry basis).

Without being bound by theory, it is believed that after batteryformation, the resulting paste has a smaller crystal structure andtherefore a higher surface area after curing when compared toconventional positive active material pastes. Furthermore, the inclusionof a metal additive, such as tin, in a weight ratio of about 900:1 canlower the α-PbO₂ to β-PbO₂ ratio of the formed battery to between about0.8 and 1.0, resulting in a battery with both high initial capacity andlong battery life.

The metal additive is generally provided as a metal sulfate in thepositive active material paste prior to formation. Suitable sulfatesother than tin sulfate may include sulfates of zinc (ZnSO₄), titaniumoxide (TiOSO₄), calcium (CaSO₄), potassium (K₂SO₄), bismuth (Bi₂(SO₄)₃)and indium (In₂(SO₄)₃).

Another embodiment of the invention is directed to a method forpreparing a positive active material paste for a flooded deep dischargelead-acid battery of the type that includes lead-antimony alloy grids.Such a method includes mixing lead oxide, a binder such as polyesterfiber, and a sulfate additive to form a dry mixture, adding water to thedry mixture and wet-mixing the resulting mixture. Acid is then added toform the positive active material paste.

In another embodiment of the present invention, a flooded deep dischargelead-acid battery includes the positive active material paste. Such aflooded deep discharge lead-acid battery includes a positive electrodegrid alloyed with antimony. The positive active material paste asdescribed above is applied to the positive electrode grid. In oneembodiment, for example, the positive electrode grid includes from about2 to about 11 wt % antimony. In another embodiment, the positiveelectrode grid includes from about 2 to about 6 wt % antimony. Whilesome amount of antimony is desirable to improve the mechanicalcharacteristics of the grid, if too much antimony is added, it can causeundesirable gassing of the finished battery, and can also drive up thecost of the grid. Consequently, there are benefits to alloys with lowantimony content.

When compared to a conventional flooded deep discharge lead-acid batteryof similar size and weight that does not include a metal additive in thepositive active material paste, a flooded deep discharge lead-acidbattery that includes a metal additive in the positive active materialpaste tends to retain a higher capacity over the life of the battery.Therefore, a battery of the present invention can provide higher totalpower output over the battery's life compared to a conventional battery.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present inventionwill be better understood by reference to the following detaileddescription when considered in conjunction with the attached drawings,in which:

FIG. 1 is a schematic sectional view of a flooded deep dischargelead-acid battery according to one embodiment of the present invention;and

FIGS. 2 through 4 are graphs comparing the cycle life of flooded deepdischarge lead-acid batteries according to embodiments of the presentinvention to a control battery in which no additive is used.

DETAILED DESCRIPTION

According to one embodiment of the invention, a positive active materialpaste for a flooded deep discharge lead-acid battery includes leadoxide, a sulfate additive, and an aqueous acid solution. The sulfateadditive may be any suitable metal or metal oxide sulfate compound,nonlimiting examples of which include SnSO₄, ZnSO₄, TiOSO₄, CaSO₄,K₂SO₄, Bi₂(SO₄)₃ and In₂(SO₄)₃.

According to embodiments of the invention, enough sulfate additive isprovided to the paste to yield a lead to metal (or metal oxide) molarratio ranging from about 90:1 to about 1000:1, and in one embodiment,for examples the molar ratio of lead to the metal (or metal oxide)ranges from about 99:1 to about 997:1. In one exemplary embodiment,enough additive is supplied such that the lead to metal (or metal oxide)molar ratio of the positive active material paste is greater than about450:1. In another embodiment, the lead to metal (or metal oxide) molarratio of the positive active material paste is between about 450:1 andabout 650:1. In yet another embodiment, the lead to metal additive molarratio of the positive active material paste is about 500:1.

In some embodiments of the invention, enough sulfate additive isprovided to the paste to yield a lead to metal (or metal oxide) weightratio ranging from about 170:1 to about 1750:1, and in one embodiment,for example the weight ratio of lead to the metal (or metal oxide)ranges from about 173:1 to about 1741:1. In one exemplary embodiment,enough additive is supplied such that the lead to metal (or metal oxide)weight ratio of the positive active material paste is greater than about750:1. In another embodiment, the lead to metal (or metal oxide) weightratio of the positive active material paste is between about 750:1 andabout 1150:1. In yet another embodiment, the lead to metal additivemolar ratio of the positive active material paste is about 870:1.

For embodiments where tin is used as the metal in the additive (i.e.,the additive is tin sulfate), the lead to tin weight ratio of thepositive active material paste may be greater than about 800:1. Inanother embodiment, the lead to tin weight ratio of the positive activematerial paste is between about 800:1 and 1100:1. In yet anotherembodiment, the lead to tin weight ratio of the positive active materialpaste is about 900:1 which corresponds to an initial amount of tinsulfate of about 0.2 wt % in the positive active material paste appliedto the positive grid prior to battery formation.

In order to provide a lead to metal (or metal oxide) molar ratio withinthe ranges discussed above, in one embodiment, the sulfate additive isprovided to the paste in an amount ranging from about 0.1 to about 1 wt% on a dry basis. In another embodiment, the sulfate additive isprovided to the paste in an amount of about 0.2 wt % on a dry basis.When using SnSO₄ as the sulfate additive, addition of more than about 1wt % in the positive paste prior to battery formation may causeundesirable tin migration to the negative electrode grid. Adding highamounts of additive may also be cost prohibitive. Based on an amount ofadditive provided to the paste of about 0.2 wt % on a dry basis, anddepending on the purity of the additive (which varies), the lead tometal (or metal oxide) molar ratio may range from about 200:1 to about825:1, and in one embodiment ranges from about 201:1 to about 823:1.

Surprisingly, according to an embodiment of the present invention, thesmall amount of metal added to the positive active material providessignificant improvements in battery performance. In addition, the smallamount of metal additive does not tend to cause any significant tinpoisoning at the negative electrode as might have been expected.

Without being bound by theory, it is believed that the inclusion of themetal additive in the positive active material paste according toembodiments of the present invention changes the crystal structure ofthe positive active material paste. As a result, it is believed that theactive material has a higher surface area on which electrochemicalreactions can occur. Accordingly, the deep discharge batteries havingthe uniform crystal structure and higher active material surface areacan withstand deep discharge with less deterioration in the chargecapacity over the life of the battery, thus improving performance.

In particular, the inclusion of tin as the metal of the additive in thepositive active paste at a lead to tin weight ratio of about 900:1 canlower the α-PbO₂ to β-PbO₂ ratio to between about 0.8 and 1.0. Such abalance of α-PbO₂ to β-PbO₂ has surprisingly shown to result in abattery with both high initial capacity and long battery life. It hasfurther been shown that at sulfate levels higher than about 0.2 wt %,the porosity of the positive active paste material increases. Such anincrease in porosity normally tends to adversely affect batteryperformance. Higher porosity indicates a higher volume of pores,enabling the electrolyte to more easily penetrate inside the activematerial solid matrix. Although this may improve initial batteryperformance, the positive active material will expand and shrink duringcharge and discharge (cycling), and the highly porous structure willdecrease the mechanical strength and shorten the cycle life of theactive material.

According to another embodiment of the present invention, a method forpreparing a positive active material paste includes mixing lead oxide, abinder such as polyester fiber, and a metal sulfate additive to form adry mixture. Water is then added to the dry mixture and the mixture iswet-mixed for a period of time. After wet-mixing, acid is added andmixing continues.

In one embodiment, as shown somewhat schematically in FIG. 1, a singlecell flooded deep discharge lead-acid battery 10 includes the positiveactive material paste as set forth above. The battery includes aplurality of positive electrode grids 12, and a plurality of negativeelectrode grids 14. Each positive electrode grid is coated with apositive active material paste 16 as set forth above to form a positiveplate. Each negative electrode grid is coated with a negative activematerial paste 18 to form a negative plate. The coated positive andnegative electrode grids are arranged in an alternating stack within abattery case 22 using a plurality of separators 24 to separate eachelectrode grid from adjacent electrode grids and prevent short circuits.A positive current collector 26 connects the positive electrode gridsand a negative current collector 28 connects the negative electrodegrids. An electrolyte solution 32 fills the battery case, and positiveand negative battery terminal posts 34, 36 extend from the battery caseto provide external electrical contact points used for charging anddischarging the battery. The battery case includes a vent 42 to allowexcess gas produced during the charge cycle to be vented to atmosphere.A vent cap 44 prevents electrolyte from spilling from the battery case.While a single cell battery is illustrated, it should be clear to one ofordinary skill in the art that the invention can be applied to multiplecell batteries as well.

According to one embodiment, the positive electrode grids are made froma lead-antimony alloy. In one embodiment, the electrode grids arealloyed with about 2 wt % to about 11 wt % antimony. In anotherembodiment, the electrode grids are alloyed with between about 2 wt %and about 6 wt % antimony.

The negative electrode grids are similarly made from an alloy of leadand antimony, but generally include less antimony than the alloy usedfor the positive electrode grids. The negative electrode grids also tendto be somewhat thinner than the positive electrode grids. Such negativeelectrode grids are well known in the art. The negative electrode gridsare coated with a negative active material that includes lead oxide andan expander as is also well known in the art. Upon battery formation,the lead oxide of the negative active material is converted to lead.

Suitable electrolytes include aqueous acid solutions. In one embodiment,the electrolyte comprises a concentrated aqueous solution of sulfuricacid having a specific gravity of about 1.1 to about 1.3 prior tobattery formation. The separators are made from any one of knownmaterials. Suitable separators are made from wood, rubber, glass fibermat, cellulose, poly vinyl chloride, and polyethylene.

According to some embodiments, the completed battery may be aged afterformation. In particular, after initial charging (i.e., batteryformation), the battery may be allowed to stand without use for an agingperiod. The aging period may range from about 2 months to about 6.5months. Batteries according to embodiments of the present invention thathave been aged after formation have surprisingly exhibited betterresults than their non-aged counterparts. These results are shown inFIG. 2, discussed in detail below relative to Examples 2 and 3.

The present invention will now be described with reference to thefollowing examples. These examples are provided for illustrativepurposes only, and are not intended to limit the scope of the presentinvention.

Example 1: Positive Active Material Paste and Positive Plate Formation

A positive active material paste was made by first mixing 2400 lbs oflead oxide powder and 2 lbs of polyester fiber in a mixer. To thatmixture, 4.40 lbs of tin sulfate was added while mixing continued. Then,specified amounts of water and acid were added and mixing continueduntil a positive active material paste was formed. The positive pasteincluded lead oxide, polyester fiber, water, and aqueous sulfuric acid.The paste density was about 4.5 g/cc, which is considered a high densitypaste and suitable for cycling applications. The resulting paste wasgray in color and had a tin sulfate concentration of about 0.18 wt % ona dry basis.

The positive active material paste was applied to identical positiveelectrode grids using a Mac Engineering & Equipment Co. commercialpasting machine to form pasted positive plates. The positive electrodegrids were cast using a Wirtz Manufacturing Co. grid casting machineusing a lead-antimony alloy with 4.5% antimony. Each positive electrodegrid was pasted with positive active material paste. The resultingpositive plates were then dried in a flash drying oven according to wellknown methods. The dried positive plates were then cured by a two-stepprocess in a curing chamber, first at 100% humidity for sixteen hours,and the plates were then dried under high temperature without humidityuntil the moisture content inside the plate was below 4%.

Comparative Example 1: Conventional Positive Active Material Paste andPlate Formation

A positive active material paste and positive plates identical to thosedescribed at Example 1 were made using the method described at Example 1with the exception that no metal sulfate additive was included in thepositive active material paste.

Examples 2-3: Battery Assembly

According to Examples 2 and 3, the positive plates formed according toExample 1 were assembled into twelve production batteries of the typemanufactured and sold by Trojan Battery Corporation as Model T105(3-cell, 6-volt, deep discharge lead-acid battery, a type commonly usedin electric golf cars). In other words, with the exception that thepositive plates of Example 1 were used instead of conventional positiveplates, all other components and manufacturing steps were identical tothose employed in making conventional Model T105 batteries. Inparticular, individual cell groups were formed by stacking eightpositive plates of Example 1 and nine conventional negative plates in analternating arrangement with conventional separators between them. Thenegative plates comprised negative electrode grids made from an alloy of2.75 wt % antimony in lead. Each negative electrode grid was pasted withnegative paste comprising lead oxide, deep cycle expander, polyesterfiber, water, and aqueous sulfuric acid. The negative paste density wasabout 4.3 g/cc, which represents a typical negative paste in the leadacid battery industry. The positive plates were then dried in a flashdrying oven and cured using the same procedures as were used for thenegative plates. The separators used were rubber separators made byMicroporous Products, L.P. The deep cycle expander was provided byAtomized Products Group, Inc.

The tabs of the negative plates of each cell group were welded togetherusing known procedures as were the tabs of the positive plates of eachcell group. For each battery, three cell groups were interconnected inseries as is well-known in the assembly of three-cell batteries, and thecombination of three cell groups was inserted into a battery case. Thecase was then sealed and the battery terminals were welded into place.The assembled batteries were then filled with aqueous sulfuric acid andcovers were placed over the vents. For each of Examples 2 and 3, theassembled batteries were connected in series, and within thirty minutesof filling the batteries with acid, the battery formation step wasinitiated. According to the battery formation step, a charge was appliedto the series of batteries using a constant current formation procedureto form the plates. The formation was terminated until the total chargeenergy reached about 190 to about 220% of the theoretical charge energybased on the quantity of positive active material and chargingefficiency. The final specific gravity of the aqueous sulfuric acidinside the batteries was about 1.275. The formed batteries were thenplaced on a shelf for a 21 day pre-condition period before performingcycle tests. After pre-conditioning, a number of the formed batterieswere aged on the shelf for an additional six months.

Comparative Example 2: Conventional Battery Assembly

For Comparative Example 2, batteries identical to those of Examples 2and 3 were constructed, except that the conventional positive plates ofComparative Example 1 were used in the assembly.

For a first test, six conditioned batteries of Example 2 were comparedagainst six conventional batteries of Comparative Example 2 immediatelyafter conditioning. In particular, the six batteries of Example 2 wereset up in series on one test circuit while the six batteries ofComparative Example 2 were set up in series on another test circuit. Fora second test, the six batteries of Example 3 were aged for another sixmonths before being set up in series on yet another test circuit.

For the tests, the batteries were repeatedly discharged and chargedusing standard procedures as established by Battery CouncilInternational. In particular, the batteries were discharged at aconstant 75 amps down to a cut-off voltage of 1.75 V per cell. For eachcircuit, the total discharged capacity for each discharge cycle wasdetermined in Ampere-hours. Once the batteries of a circuit weredischarged, the circuit was rested for 30 minutes before recharging.After the rest step, the batteries were recharged using a three-stepI-E-I charge profile up to 110% of the capacity discharged on theimmediately preceding discharge cycle. In this 3-step charge profile,the first step employs a constant start current in which charge currentto the batteries is maintained at a constant value (in this case 17.7 A)during the initial charge stage until the battery voltage per cellreaches a specified level (in this case 2.35 VPC). In the second step,the battery voltage is maintained at a steady voltage while beingcharged with decreasing current. In the third step, a lower constantcurrent is delivered to the batteries (in this case 4.5 A). Such acharge profile is abbreviated in this specification as “IEI 7.7A-2.35VPC-4.5 A-110%.” Once recharged, the battery circuit was restedfor two hours before being discharged. These steps were repeated untilthe batteries failed to deliver 50% of the manufacturer's rated capacityon a discharge cycle. Defective batteries may have been removed from thestring during cycle life testing, not exceeding removal of 50% of thetotal batteries in the circuit. Also, no replacement batteries wereadded during testing.

The results of the tests are shown in FIG. 2, which graphs capacity percycle against the number of cycles, where the capacity per cycle iscorrected for temperature using standardization procedures set forth byBattery Council International. FIG. 2 shows the effect of additive on 6Vgolf lead acid batteries. Batteries with additive show betterperformance than control batteries. In addition, as shown in FIG. 2, thebatteries that were aged an additional six months performedsignificantly better than their non-aged counterparts. The curve fittingwas based on the polynomial regression function of the Microsoft Excelprogram.

As illustrated by FIG. 2, the batteries of the present invention exhibitconsistently higher ampere hour discharge and sustained peak capacityfor longer periods of time. Moreover, the battery circuit usingbatteries according to Example 2 exhibited consistently higherampere-hour discharge per cycle. The Example 3 batteries have deliveredhigher performance than the Example 2 batteries. This is due to a longeraging period, which helps produce more sulfates inside the PAM (positiveactive material) matrix and improves utilization of the PAM duringcycling. The total ampere-hour capacity over the life of the testbatteries is summarized in Table 1.

TABLE 1 Total Accumulated Average Ampere- Test Cycles Ampere-Hours Hoursper cycle Example 2 512 69,763 136 Example 3 515 74,539 145 Comparative525 62,266 119 Example 2

Example 4 and Comparative Example 3

For Example 4, the positive plates formed according to Example 1 wereassembled into six production batteries of the type manufactured andsold by Trojan Battery Corporation as Model J305P (3-cell, 6-volt, deepdischarge lead-acid batteries of a type commonly used in scrubber &floor machine batteries). For Comparative Example 3, batteries identicalto those of Example 4 were constructed, except that the conventionalpositive plates of Comparative Example 1 were used in the assembly.

The results of the tests are shown in FIG. 3 which graphs capacity percycle against the number of cycles, where the capacity per cycle iscorrected for temperature using standardization procedures set forth byBattery Council International. FIG. 3 shows the effect of additive on 6Vscrubber batteries. Batteries with additive show better performance thanthe control batteries. The curve fitting was based on the polynomialregression function of the Microsoft Excel program.

As illustrated by FIG. 3, the batteries of the present invention exhibitconsistently higher ampere hour discharge and sustained peak capacityfor longer periods of time. Moreover, these test results re-confirm theconclusions gained from FIG. 2 that the batteries of the presentinvention show similar effects and benefits on different models of leadacid battery products. The total ampere-hour capacity over the life ofthe test batteries is summarized in Table 2.

TABLE 2 Total Accumulated Average Ampere- Test Cycles Ampere-Hours Hoursper cycle Example 4 392 78,695 201 Comparative 315 61,268 194 Example 3

Examples 5-11 and Comparative Example 4

For Examples 5-11, positive active material pastes were preparedincluding various additive salts as set forth in Table 3. ForComparative Example 4, a conventional positive active material paste wasprepared without any additive. The positive active material pastes wereprepared in a lab scale mixer. Each positive active material paste wasmade by first mixing 10 lbs of lead oxide powder and 3.8 grams ofpolyester fiber in a mixer. To that mixture, 9.08 grams of additive wasadded while mixing continued. Then, water was added to the dry mixtureand mixing continued for one minute. Finally, an aqueous solution ofsulfuric acid was added and mixing continued until a positive activematerial paste was formed. The resulting paste was gray in color and hadan additive concentration of about 0.20 wt % on a dry basis.

The positive active material pastes prepared above were manually appliedto substantially identical positive electrode grids to form pastedpositive plates. The positive electrode grids were made as described inExample 1, and were used in a 2-volt single cell jar for cycle lifetesting. Each positive electrode grid weighed 144+/−5 grams and waspasted with 278+/−3 grams of positive active material paste. Theresulting positive plates were then cured by a two-step process in a labscale curing chamber.

TABLE 3 Metal (or Metal Metal Oxide) (or Salt Amount Pb:Metal (or MetalMetal (or Metal (wt % Metal Oxide) Example Oxide) Oxide) Salt dry basis)Molar Ratio Example 5 Sn SnSO₄ 0.20% 500 Example 6 TiO TiOSO₄ 0.20% 334Example 7 Ca CaSO₄ 0.20% 314 Example 8 K K₂SO₄ 0.20% 201 Example 9 InIn₂(SO₄)₃•xH₂O 0.20% 729 Example 10 Zn ZnSO₄•7H₂O 0.20% 663 Example 11Bi Bi₂(SO₄)₃ 0.20% 823

The single cells made for Examples 5-11 and Comparative Example 4 weretested in the same manner as the Example 2 batteries. The totalampere-hour capacity over the life of the test batteries is summarizedin Table 4.

TABLE 4 Metal (or Metal Total Accumulated Average Ampere- Example Oxide)Cycle Ampere-Hours Hours per cycle Example 5* Sn 169 23,101 137 Example6 TiO 200 23,068 115 Example 7 Ca 200 25,938 130 Example 8 K 200 25,681128 Example 9 In 200 25,980 130 Example 10 Zn 200 24,667 123 Example 11Bi 200 24,996 125 Comparative N/A 200 25,630 128 Example 4 *Testing wasstopped prematurely due to equipment failure.

Examples 12 and 13 and Comparative Example 5

For Examples 12 and 13, positive active material pastes were preparedincluding various tin sulfate contents as set forth in Table 5. Thequantities of acid and water needed to be adjusted as the additivecontent increased. The density of the positive paste changed due to theadjustment of acid/water quantity. The densities of the positive pastefor each mix varied from about 4.3 to about 4.7 g/cc. For ComparativeExample 5, a conventional positive active material paste was preparedwithout any metal additive. The positive active material pastes preparedas above were manually applied to substantially identical positiveelectrode grids to form pasted positive plates. The positive electrodegrids were made as described in Example 1, and were used in 2-voltsingle cell jars for cycle life testing. Each positive electrode gridweighed 144+/−5 grams and was pasted with 278+/−3 grams of positiveactive material paste. The resulting positive plates were then curedunder the same conditions as Examples 5-11.

TABLE 5 Tin Sulfate Amount Pb:Sn Pb:Sn Example (wt % dry basis) WeightRatio Molar Ratio Example 12 0.2% 870 498 Example 13 1.0% 173  99Comparative 0.0% N/A N/A Example 5

The single cells made for Examples 12 and 13 and Comparative Example 5were tested in the same manner as the Example 2 batteries. The totalampere-hour capacity over the life of the test batteries is summarizedin Table 6. The results of the tests are shown in FIG. 4 which graphscapacity per cycle against the number of cycles, where the capacity percycle is corrected for temperature as mentioned above. As illustrated byFIG. 4, the batteries of the present invention exhibit consistentlyhigher ampere hour discharge energy than conventional batteries.

TABLE 6 Tin Sulfate Total Amount Accumulated Average Ampere- Example (wt% dry) Cycle Ampere-Hours Hours per cycle Example 12* 0.2% 169 23,101137 Example 13 1.0% 200 29,296 147 Comparative 0.0% 200 25,630 128Example 5 *Testing was stopped prematurely due to equipment failure.

While the present invention has been illustrated and described withreference to certain exemplary embodiments, those of ordinary skill inthe art would appreciate that various modifications and changes can bemade to the described embodiments without departing from the spirit andscope of the present invention, as defined in the following claims.

What is claimed is:
 1. A method for making a flooded lead-acid batterycomprising: casting a plurality of positive electrode grids from a firstlead-antimony alloy; casting a plurality of negative electrode gridsfrom a second lead-antimony alloy, applying a negative active materialpaste to the plurality of negative electrode grids to form a pluralityof negative plates, the negative active material comprising lead oxide;applying a positive active material paste to the plurality of positiveelectrode grids to form a plurality of positive plates, the positiveactive material paste comprising lead oxide, a binder, and a metalsulfate comprising a metal selected from the group consisting of tin,zinc, titanium, calcium, potassium, bismuth, indium, and combinationsthereof, wherein the molar ratio of lead to the metal in the positiveactive material paste is from about from about 450:1 to about 650:1;arranging the plurality of positive and negative plates in analternating arrangement in a battery case with the positive and negativeplates separated from one another by a plurality of separators; addingan aqueous electrolyte to the battery case; and applying a charge acrossthe positive and negative plates, thereby forming the flooded lead-acidbattery.
 2. The method of claim 1 wherein the metal sulfate is tinsulfate, and the tin sulfate is present in the positive active materialpaste in an amount from about 0.1 wt % to about 1 wt % on a dry basis.3. The method of claim 2 wherein the tin sulfate is present in thepositive active material paste in an amount from about 0.15 wt % toabout 0.2 wt % on a dry basis.
 4. The method of claim 2 wherein the tinsulfate is present in the positive active material paste in an amount ofabout 0.18 wt % on a dry basis.
 5. The method of claim 1 furthercomprising aging the flooded lead-acid battery for a period of time fromabout 2 months to about 6½ months.
 6. The method of claim 1 wherein thefirst and second lead-antimony alloys comprise between about 2 wt % and6 wt % of antimony.
 7. The method of claim 6 wherein the secondlead-antimony alloy contains a lower percentage of antimony than thefirst lead-antimony alloy.
 8. A method for making a flooded lead-acidbattery comprising: casting a plurality of positive electrode grids froma first lead-antimony alloy; casting a plurality of negative electrodegrids from a second lead-antimony alloy, wherein the secondlead-antimony alloy contains a lower percentage of antimony than thefirst lead-antimony alloy; applying a negative active material paste tothe plurality of negative electrode grids to form a plurality ofnegative plates, the negative active material comprising lead oxide;applying a positive active material paste to the plurality of positiveelectrode grids to form a plurality of positive plates, the positiveactive material paste comprising lead oxide, a binder, and tin sulfate,wherein the tin sulfate is present in the positive active material pastein an amount from about 0.1 wt % to about 1 wt % on a dry basis;arranging the plurality of positive and negative plates in analternating arrangement in a battery case with the positive and negativeplates separated from one another by a plurality of separators; addingan aqueous electrolyte to the battery case; and applying a charge acrossthe positive and negative plates, thereby forming the flooded lead-acidbattery.
 9. The method of claim 8 wherein the tin sulfate is present inthe positive active material paste in an amount from about 0.15 wt % toabout 0.2 wt % on a dry basis.
 10. The method of claim 8 wherein the tinsulfate is present in the positive active material paste in an amount ofabout 0.18 wt % on a dry basis.
 11. The method of claim 8 furthercomprising aging the flooded lead-acid battery for a period of time fromabout 2 months to about 6½ months.
 12. The method of claim 8 wherein thefirst and second lead-antimony alloys comprise between about 2 wt % and6 wt % of antimony.
 13. A positive plate for a flooded lead-acid batterycomprising an unclad cast electrode grid made of a lead-antimony alloycomprising from about 2 to about 11 wt % antimony, wherein the uncladcast electrode grid is coated with a positive active material pastecomprising lead oxide, a binder, and tin sulfate, wherein the tinsulfate is present in the positive active material paste in an amountfrom about 0.1 wt % to about 1 wt % on a dry basis.
 14. The positiveplate of claim 13 wherein the tin sulfate is present in the positiveactive material paste in an amount from about 0.15 wt % to about 0.2 wt% on a dry basis.
 15. The positive plate of claim 13 wherein the tinsulfate is present in the positive active material paste in an amount ofabout 0.18 wt % on a dry basis.
 16. The positive plate of claim 13wherein lead-antimony alloy comprises between about 2 wt % and 6 wt % ofantimony.
 17. A method for making a positive plate for a floodedlead-acid battery comprising: casting a positive electrode grid from alead-antimony alloy, wherein the lead-antimony alloy comprises betweenabout 2 wt % and 6 wt % of antimony; applying a positive active materialpaste to the cast positive electrode grid, the positive active materialpaste comprising lead oxide, a binder, and tin sulfate, wherein the tinsulfate is present the positive active material paste in an amount fromabout 0.1 wt % to about 1 wt % on a dry basis.
 18. The method of claim17 wherein the tin sulfate is present in the positive active materialpaste in an amount from about 0.15 wt % to about 0.2 wt % on a drybasis.
 19. The method of claim 17 wherein the tin sulfate is present inthe positive active material paste in an amount of about 0.18 wt % on adry basis.